Shiplifts are used to dry dock and launch ships. Shiplifts typically include a structural platform that is lifted and lowered by hoists. Existing shiplift platform designs typically have arms that reach underneath piers on either side of the platform so that the hoists (e.g., chain jacks or winches) can be connected to the shiplift platform structure via chains or wire ropes. These hoists operate to lift and lower the shiplift platform, with or without a ship on it. Typically, the shiplift platform is lowered underwater, a ship is floated above the shiplift platform, and the shiplift platform and ship are then lifted.
A problem with such designs is that, when the shiplift platform is being installed onto the pier, arms of the shiplift platform must be positioned between the pilings that hold up the pier. Two methods of achieving this include: 1) the use of removable end connections that are removed from the shiplift platform while the shiplift platform is being floated into position adjacent the pier, and then installed onto the shiplift platform after the shiplift platform has been floated into position adjacent to the pier for connection between the shiplift platform and the hoists; and 2) tipping the shiplift platform upwards to a steep angle using cranes, and then lowering the shiplift platform into position adjacent to the pier. Both of these methods offer challenges.
Shiplift end weldments of shiplift platforms must overcome several design challenges. The structure must extend under the support pile caps of the pier to connect with the lifting devices (i.e., hoists) supported on the pile caps. This connection typically requires a change of cross section in the main transverse girder of the shiplift platform to allow the top of the shiplift platform structure to be flush with the top of the pile cap. Prior shiplift platform designs have utilized weldments with complex geometry and multiple heavy plates to solve these two design challenges.
Shiplift platform designs using fixed end weldments also have installation challenges. The projecting end weldments are wider than the pile spacing and shiplift platform opening, which prevents the shiplift platform from being installed safely and efficiently at a pier. At least some such prior field installations of rigid shiplift platforms have required the performance of costly, in place welding and painting operations.
Shiplift platform sections, rigid or articulated, are sometimes installed by high-risk, heavy tandem lifts employing multiple cranes. During such installations, each shiplift platform section is typically tilted to 30° or more to allow the end weldments to pass through the openings between pile caps of the pier. While articulated shiplift platform designs reduce the amount of on-site field welding and painting operations, such designs still require high-risk, heavy tandem lifts during installation.